AngularJS function returning promise with required parameter

Question

Simple question. I have build this function:

// Gets the kit by id or slug
var _getKit = function (id) {

    // Try to get our kit using our shared service
    return sharedKitService.get(id).then(function (response) {

        // Assign the response to our service
        service.models.kit = response;

        // Return our response
        return response;
    })
};

and I want to add a check to the function to be something like this:

// Gets the kit by id or slug
var _getKit = function (id) {

    // If we have no id, exit the function
    if (!id)
        return;

    // Try to get our kit using our shared service
    return sharedKitService.get(id).then(function (response) {

        // Assign the response to our service
        service.models.kit = response;

        // Return our response
        return response;
    })
};

But I know that won't work because if there is no id then the function will no longer produce a promise. I know I could do something like this:

// Gets the kit by id or slug
var _getKit = function (id) {

    // If we have no id
    if (!id) {

        // Defer our promise
        var deferred = $q.derfer();

        // Reject our promise
        deferred.reject();

        // Return our promise
        return deferred.promise;
    }

    // Try to get our kit using our shared service
    return sharedKitService.get(id).then(function (response) {

        // Assign the response to our service
        service.models.kit = response;

        // Return our response
        return response;
    })
};

but this seems like overkill. Is there an easier way to do this?

Answer 1

You can write your function as below for shorter purpose.

// Gets the kit by id or slug
var _getKit = function (id) {
    var deferred = $q.defer();
    // If we have no id
    if (!id) {
        // Reject our promise
        deferred.reject();
    } else {
        sharedKitService.get(id).then(function (response) {
            // Assign the response to our service
            service.models.kit = response;

            // Return our response
            deferred.resolve(response);
        });
    }
    return deferred.promise;
};

Answer 2

From the Angular docs:

Just return $q.reject(reason). This returns Promise which is instantly rejected

Answer 3

you can simply use

$q.reject();